1. Field of the Invention
The present invention relates to an improvement in an optical fiber system for transmitting a laser beam.
2. Description of the Prior Art
Recently, power transmitting optical fibers have become widely used in industry, medicine and the like. The term "power" includes high laser power. Typical lasers include carbon dioxide lasers, YAG lasers, Ar lasers and the like. YAG lasers, Ar lasers and the like, can transmit through a quartz glass fiber. However, light from a carbon dioxide laser can not be transmitted through a quartz fiber because of its long wave length. Although it can be transmitted by means of a mirror, the structure of articulation is so complicated to make use difficult. However, crystalline fibers of silver halide, thallium halide, and alkali halide can transmit the light of the carbon dioxide laser.
Advantages in light power transmission by means of optical fibers are such that light can be conducted into even a narrow space and along a complicated path having many bent portions to irradiate any object. This is because an optical fiber has superior characteristics such as small diameter, flexibility and so on.
Although one end of the optical fiber is connected with a laser source, the other end is often exposed because it is necessary to emit a laser beam therefrom toward an object to be irradiated with the laser beam. However, the end from which the laser beam is emitted (hereinafter simply referred to as "a light-emitting end"), is often inserted into a narrow space, into a space having many bent portions, or into a space filled with a liquid or a solid, so that the light-emitting end is apt to be damaged. Foreign matter, such as dust, drops of water, blood, or the like, may adhere on the light-emitting end of an optical fiber used for power-transmitting a laser beam, depending on the environment in which the optical fiber is used.
If a laser beam is passed through an optical fiber with foreign matter adhered on its light-emitting end, the foreign matter is heated by the laser beam and sometimes burnt and stuck on the end surface of the optical fiber. If this happens, transmission quality deteriorates, and the temperature sharply rises as the laser beam energy is absorbed by the foreign matter, damaging the light-emitting end of the optical fiber.
Conventionally, an opening/closing cover has been provided at the light-emitting end of an optical fiber to prevent such accidents. The cover is opened only when a laser beam is emitted and closed when no laser beam is being emitted. Thus, the light-emitting end of the optical fiber is being protected by the cover when no laser beam is emitted. However, the laser beam per se has no power to prevent dust, blood, drops of water, or the like, from adhering onto the light-emitting end. When the light-emitting end of the optical fiber is put in an environment containing liquid, such as water drops, blood, or the like, the liquid may adhere to the light-emitting end when the protecting cover is opened during emission. This deteriorates the transmittivity at the end surface to extremely reduce the treating capability of the laser beam. Further, the light-emitting end may be sometimes broken because the end surface is sharply heated. There are two kinds of opening/closing mechanisms, one being of the type provided at the forward end of an optical fiber and the other being of the type provided in the back of an optical fiber and controlled remotely.
An opening/closing mechanism at the forward end of an optical fiber is provided with a motor, a reduction gear, gearing, and so on, attached at that end to open and close the cover by the forward and backward rotation of the motor. In such a cover opening/closing mechanism, it is necessary to attach a motor, a reduction gear, a gearing, and so on, at a light-emitting end of an optical fiber, so that the end of the optical fiber becomes bulky, loses flexibility and becomes heavy. Moreover, it is necessary to incorporate electrical conductive lead wires in the optical fiber as a power feeder and a signal line for the motor, so that the structure of the optical fiber becomes complicated.
Thus, if a prime mover is attached at the light-emitting end, the light-emitting end becomes heavy and bulky. Therefore a mechanism has been proposed to remotely operate the cover. In this mechanism, a motor, a reduction gear, and the like are provided not at the light-emitting end of an optical fiber but in the vicinity of the light source. A cover opening/closing portion urged in one direction by a spring and pulled in the reverse direction by a wire is provided at the forward end of the optical fiber. The motor, or the like, and the cover opening/closing portion at the forward end of the optical fiber are connected with each other by a wire extending along the optical fiber.
Thus, the mechanical structure provided at the light-emitting end of the optical fiber is reduced in size as well as in weight and becomes easier to use. The wire, however, must be provided along the fiber, so that the structure of the optical fiber becomes complicated. Also the flexibility at the intermediate portion of the optical fiber is reduced.